Ball joints have been used in automotive vehicles for long periods of time and are commonly associated with vehicle suspension and steering systems. They are used to couple two or more elements together, for example wheel hubs are generally coupled to the rest of the suspension by way of a ball joint while at the same time enabling movement of these elements with respect to each other in a number of directions. Ball joints basically include a metal ball that is supported within a cage or socket. Typically the space between the ball and the socket is filled with grease so as to reduce wear and it is common to place a rubber seal over the ball joint to help keep water and dirt out. Occasionally rubber seals fail and as a result, water, dirt and/or other impurities may enter into the ball joint, and grease may also leak out of the ball joint which in turn reduces the usable life of the ball joint. Ball joints can also fail as a result of impact forces such as when the wheel strikes a pot hole or curb for example. Corrosion, wear, damage and/or failure of ball joints is often manifest audibly and/or tacitly. Indications that a typical ball joint may be failing include clicking, popping or snapping noises. These noises may develop into a squeaking sound when driving the vehicle, during acceleration and/or also when hitting bumps. Another indication of ball joint failure may be ‘thud’ noises that come from the suspension when going over bumps. Ball joints in which the grease or other lubricant has leaked can be recognized by a dramatic increase of friction causing the steering to stick or become difficult.
The results of ball joint failure can be dangerous since the angle of the wheel becomes unconstrained, thus causing loss of control of the automobile. The lack of control of the steering angle of a tire can cause damage to the tire as well as other parts of the vehicle.
Over the past 10 years many improvements have been made in ride technology with advances in electronic and smart systems. Although these systems enhance the operation of automobiles, they also tend to reduce the audible and tactile effects caused, for example, by corrosion, wear, damage and/or failure of ball joints and thus make it much more difficult to detect worn or damaged ball joints. It is possible that a driver may not even notice that a ball joint has been damaged and thus will continue driving the automobile in this state.
A method is known from DE 10 2008 041 050 A1 for measuring the wear of a ball and socket joint. For this purpose, a magnetic field parameter is measured with a magnetic field sensor at a point of time, in which either a force or no force is acting on a ball stud of a ball joint. The measured magnetic field parameter is then transmitted from the magnetic field sensor to a control unit for evaluation. By evaluating the measured sensor signal, the wear condition of the ball and socket joint can be determined. Specifically, the ball and socket joint includes a ball stud having a ball that is pivotally and rotatably supported by a ball socket. The ball and socket joint includes an angle measuring device having a magnet that is fixed to one of the ball and the ball socket, and a magnetic field sensor that is fixed to the other of the ball and the ball socket. The magnetic field sensor measures the intensity of the magnetic field generated by the magnet in at least one spatial direction at a first time point when the ball and socket joint is under a first load. The magnetic field sensor then measures the intensity of the magnetic field generated by the magnet in the same spatial direction at a second time point when the ball and socket joint is under a second load. As the position of the ball relative to the ball socket depends on the loads acting on the ball and socket joint, the magnetic field intensity measurements are then evaluated with reference to the loads placed the ball and socket joint to determine the wear condition of the ball and socket joint. Although this ball and socket joint may be beneficial for its intended purpose, the sensor merely detects the position of the ball with respect to the socket as the magnet moves in relation to the sensor and does not determine wear or failure of the ball joint.